There are many factors that affect pitch balance, including throttle reduction, flaps retraction, landing gear retraction and center of gravity change. The following are introduced: add or reduce the throttle will change the size of pull or thrust, so as to change the size of pull torque or thrust torque, aviation vibration balance instrument affects the pitch balance of the aircraft. It needs to be pointed out that, after the throttle is reduced, the aircraft is upward or downward, can not only look at the pull torque or thrust torque on the pitch balance, need to comprehensively consider the throttle caused by the wing, horizontal tail and other changes in torque.

The retracting of flaps will cause the change of lift and pitching moment, which will affect the pitching balance. For example, when flaps are lowered, on the one hand, the lift force and pressure center of the wing move backward, which increases the downward torque of the aircraft, trying to keep the nose down. On the other hand, due to the increase of the downwash Angle of airflow over the wing, the negative Angle of attack of the horizontal tail wing, the negative lift force and the upward moment of the aircraft increase, trying to make the aircraft head upward. After flapping, whether the downward moment is large or the upward moment is large depends on the type of flap, the Angle of lowering, the height of the horizontal tail position, the size of the area and other characteristics.

When the flaps are lowered, the nose is lifted or lowered, depending on which is greater or lesser, and whether lift is ultimately increased or decreased. When the flaps are lowered, if the upward-turning moment increases, the Angle of attack increases and the lift increases. At this point, the plane naturally turns into an upward curve and flips its nose up. But if you lower the flaps and increase the downhand torque and decrease the Angle of attack, there are two possibilities. One is that when the Angle of attack decreases more, the lift decreases, and the plane turns into a downward curve and bends down. One is that the Angle of attack decreases only a little, lift still increases with flaps, and the plane still turns up in an upward curve, causing the nose to tilt up.